The present invention relates to the field of measuring temperature in high temperature environments, and more particularly to measuring high temperatures with thin film thermocouples. Most particularly, the invention relates to thin film thermocouples bonded to ceramic substrates exposed to high temperatures.
Internal combustion engines generally operate at high temperature. The temperatures in the combustion chambers are especially high. Presently, ceramic insulating materials are incorporated as thermal barrier coatings or linings in internal combustion engines in order to minimize cooling losses and achieve higher engine operating efficiency and higher power to weight ratios.
Ceramic materials including aluminum oxide and partially stabilized zirconia may be employed for the thermal barrier coatings or linings. The effective use of these materials as thermal barrier coatings or linings requires detailed knowledge of the temperature characteristics of the coatings or linings under combustion conditions.
To obtain the desired detailed knowledge of the temperature characteristics, heat flux meters based on sandwiched thin film thermocouples can be used. Such thermocouples provide detailed heat transfer information with respect to heat transfer in the engine.
Prior art thin film thermocouples include a nickel-iron thermocouple developed for gun barrel measurements. However, these sensors lack reasonable durability in diesel engines and do not accurately reproduce the thermal environment of the engine having thermal barrier coatings.
The development of sputtered thin film thermocouples based on noble metals has led to thermocouples that can operate in the harsh environment of a combustion chamber. This is due, in part, to the stability of the noble metals in the harsh environment. Such noble metal thin film thermocouples also provide fast and accurate response due to their low mass (less than 1 mg) and their flexibility of application to a surface where the thermal measurement is needed. See:
(1) H. P. Grant, J. S. Przybyszewski, and R. G. Claing, NASA CR-165201, 17 Mar. 1981;
(2) H. P. Grant, J. S. Przybyszewski, and R. G. Claing, and W. L. Anderson, NASA CR-165476, 11 Jan. 1982;
(3) K. G. Kreider, S. Semancik, and C. Osen, Advanced Thin Film Thermocouples, IR84-2949 (National Bureau of Standards, Washington, D.C., 1984); and
(4) K. G. Kreider and S. Semancik, J. Vac. Technol. A 3, 2582 (1985).
There is, however, a significant problem in the application of noble metal thin film thermocouples in measuring the surface temperature of a ceramic, especially a thermal barrier coating in an internal combustion engine, up to 700 Deg. C.; and that problem is the poor adherence of the thermocouple to the ceramic. It would be desirable, therefore, to provide a method of making thin film noble metal thermocouples that readily adhere to ceramic substrates subject to high temperatures. More particularly, it would be desirable to provide a method of making thin film noble metal thermocouples that readily adhere to ceramic substrates subject to high temperatures. More particularly, it would be desirable to provide a method for improving the adherence of thin film noble metal thermocouples to ceramic thermal barrier coatings or linings used in internal combustion engines, especially diesel engines.
In a technical program of the Society of Automotive Engineers, a paper was presented entitled "Heat Transfer in a Cooled and Insulated Engine" by Thomas Morrell from Integral Technologies, Inc.. The paper was published approximately Feb. 25, 1989. The paper reported that certain undisclosed thermocouples allowed the temperature measurement of the inside of a diesel engine lined with ceramics. However, no disclosure was made of the method of bonding the thermocouple to the ceramic engine lining.
It is noted that in an A.I.Ch.E. symposium on sensors, in October 1988, the method of the present invention, of adhering a thin film noble metal thermocouple to a ceramic lining in an internal combustion engine, was disclosed.